1. Field of the Invention
The present invention relates to high-frequency signal lines and methods for producing base layers with signal lines, and more particularly, the present invention relates to a flexible high-frequency signal line and a method for producing a base layer with a signal line.
2. Description of the Related Art
As a conventional high-frequency signal line, a high-frequency signal line described in, for example, Japanese Utility Model No. 3173143, is known. FIG. 11 is an exploded view of the high-frequency signal line 500 described in Japanese Utility Model No. 3173143.
The high-frequency signal line 500 includes a laminate 502, a signal line 506, and ground conductors 508 and 510, as shown in FIG. 11. The laminate 502 is formed by laminating dielectric sheets 504a to 504c. The signal line 506 is provided on the dielectric sheet 504b. The ground conductors 508 and 510 are provided on the dielectric sheets 504a and 504c, respectively. Accordingly, the signal line 506 is positioned between the ground conductors 508 and 510 in the vertical direction. That is, the signal line 506 and the ground conductors 508 and 510 form a stripline structure.
Furthermore, the ground conductor 508 has a plurality of openings 512 overlapping with the signal line 506. Moreover, the overlap of the signal line 506 with the opening 512 is wider than the overlap of the signal line 506 with the ground conductor 508.
Incidentally, in the case of the high-frequency signal line 500 described in Japanese Utility Model No. 3173143, the signal line 506 is prone to breakage, as will be described below. More specifically, at the time of production of the high-frequency signal line 500, a large-sized mother dielectric sheet having its entire surface coated with a conductor film is wound on a supply roll. The conductor film is patterned between the supply roll and a take-up roll while the mother dielectric sheet is being wound up on the take-up roll. As a result, a plurality of signal lines 506 are formed on the mother dielectric sheet.
Here, there is a tensile force generated between the supply roll and the take-up roll. Accordingly, in the case where the signal lines 506 extend parallel to the direction in which the mother dielectric sheet is transported, the signal lines 506 are pulled in directions in which they can be stretched. The signal line 506 has narrow and wide portions. The signal line 506 can be stretched in the narrow portions more than in the wide portions. On the other hand, the signal line 506 has less strength in the narrow portions than in the wide portions. Therefore, when the signal line 506 is pulled in directions in which it can be stretched, the signal line 506 might be broken in narrow portions.